As imaging techniques of MRI, there are techniques for obtaining three-dimensional angiograms without using any contrast medium (Patent documents 1 and 2). In such non-contrast angiography, it is desirable to carry out cardiac gated imaging in order to enhance artery or vein depiction ability, and in this case, echo signal acquisition is triggered with signals obtained on the basis of pulsation of the heart (for example, R waves), but started with a certain delay time. Specifically, echo signals are obtained only in the diastolic or systolic phase of the heart. However, the diastolic and systolic phases of the heart do not necessarily occur with constant cycles. Therefore, when a predetermined number of echo signals are obtained, image quality may be degraded, or there may be waste time not used for the measurement after acquisition of echo signals. Accordingly, such imaging methods as mentioned above suffer from such problems as degradation of image quality and prolongation of the measurement time for measuring a predetermined number of echo signals required for reconstructing a three-dimensional image.
Further, a technique for imaging with changing delay time for imaging of the diastolic phase on the real time basis has been proposed in Non-patent document 1. According to this technique, it is possible to prevent degradation of image quality due to the change of the delay time, but it cannot eliminate the aforementioned problems caused by the change between the diastolic and systolic phases.
Moreover, in the conventional non-contrast 3D imaging, a multi echo type sequence is generally used, and a step of collecting echo signals, in which one of phase encoding and slice encoding is fixed and another is changed, is repeated while changing the one. Therefore, influence of the T2 decay necessarily appears in either one of the phase encoding direction or slice encoding direction. Imaging with such data including influence of the T2 decay results in blurred MRA image in the phase encoding direction or the slice encoding direction, which may inhibit correct diagnosis.
In addition, although it is not a technique for angiography, as a technique for three-dimensional imaging, an imaging technique using sampling of three-dimensional k-space data circularly or elliptically, not rectangularly, is disclosed in Non-patent document 2. Such rectangular sampling is a technique of performing sampling along a trajectory parallel to one axis of the coordinates of the k-space, and it is called orthogonal system sampling.